import math

class Vector3D:
    def __init__(self, x, y, z, l):
        self.x = x
        self.y = y
        self.z = z
        self.l = l

    def length(self):
        return math.sqrt(self.x ** 2 + self.y ** 2 + self.z ** 2)

    def velocity_decomposition(self):
        length = self.length()
        if length == 0:
            return Vector3D(0, 0, 0)
        else:
            return Vector3D(self.x * self.l / length, self.y * self.l / length, self.z * self.l / length,1)
